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From: said assemlal <[email protected]>
To: Christoph Berg <[email protected]>
To: PostgreSQL Hackers <[email protected]>
Subject: Re: Available disk space per tablespace
Date: Thu, 24 Apr 2025 15:26:24 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>

Hi,

I also tested the patch on Linux mint 22.1 with the btrfs and ext4 
partitions. I generated some data and the outcome looks good:

postgres=# \db+
                                                    List of tablespaces
        Name       |  Owner   |         Location          | Access 
privileges | Options |  Size   |  Free   | Description
------------------+----------+---------------------------+-------------------+---------+---------+---------+-------------
  pg_default       | postgres | |                   |         | 1972 MB 
| 29 GB   |
  pg_global        | postgres | |                   |         | 556 kB  
| 29 GB   |
  tablespace_test2 | postgres | /media/said/queryme/pgsql 
|                   |         | 3147 MB | 1736 GB |


Numbers are the same as if I were executing the command: df -h

tablespace_test2 was the ext4 partition on usb stick.

Numbers are correct.

Said

On 2025-03-13 14 h 10, Christoph Berg wrote:
> Hi,
>
> I'm picking up a 5 year old patch again:
> https://www.postgresql.org/message-id/flat/20191108132419.GG8017%40msg.df7cb.de
>
> Users will be interested in knowing how much extra data they can load
> into a database, but PG currently does not expose that number. This
> patch introduces a new function pg_tablespace_avail() that takes a
> tablespace name or oid, and returns the number of bytes "available"
> there. This is the number without any reserved blocks (Unix, f_avail)
> or available to the current user (Windows).
>
> (This is not meant to replace a full-fledged OS monitoring system that
> has much more numbers about disks and everything, it is filling a UX
> gap.)
>
> Compared to the last patch, this just returns a single number so it's
> easier to use - total space isn't all that interesting, we just return
> the number the user wants.
>
> The free space is included in \db+ output:
>
> postgres =# \db+
>                                       List of tablespaces
>      Name    │ Owner │ Location │ Access privileges │ Options │  Size   │  Free  │ Description
> ────────────┼───────┼──────────┼───────────────────┼─────────┼─────────┼────────┼─────────────
>   pg_default │ myon  │          │ ∅                 │ ∅       │ 23 MB   │ 538 GB │ ∅
>   pg_global  │ myon  │          │ ∅                 │ ∅       │ 556 kB  │ 538 GB │ ∅
>   spc        │ myon  │ /tmp/spc │ ∅                 │ ∅       │ 0 bytes │ 31 GB  │ ∅
> (3 rows)
>
> The patch has also been tested on Windows.
>
> TODO: Figure out which systems need statfs() vs statvfs()
>
> Christoph

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